Why are sprints so fast??

i seen five differnt targa lx's go up against a sprint in a race, and the targas get beat every time. All the targa lx's and the sprint are stock. For some odd reason, the sprint is able to get about a 15 ft. lead ahead of the targa lx's each time it races themoff the line. why does the sprint accelerate so much quicker? (it has nothing to do with the weight of the mopeds or riders.)

RE: Why are sprints so fast??

Reeperette /

The Gear Ranging (done by springs in the centrifugal clutch) is different

My old single-speed Puch Austro-Daimler would pulverize most bikes on takeoff, but after a 1/4mile, all I would be seeing was thier tail lights.

Most 50cc motors are geared for a balance between takeoff power (low end) and eventual top speed (high end) with a heavy emphasis on top speed, which is good since the general public thinks 50mph in a 30mph is ok (which SUCKS, when you have to drive in that area).

But the other school of thought, is not getting rear-ended by fourwheelers when taking off at a greenlight, and those are geared for more takeoff power at the expense of a slightly lower eventual top speed.

Try a couple of half-mile races, if you wish to test that theory.


RE: Why are sprints so fast??

the sprint tops out at the same speed as the targas, every time!

RE: Why are sprints so fast??

Sergi Grum /


I'm from Spain, and I'm 15, but I have quite an expirience in racing and tuning mopeds. The answer is quite simple: the clutch. Without ever touching the final ratios, you can easily make the moped be quicker. An automatic clutch uses centifugal force to operate. It's like a drum brake, the interiortouches the exterior, so the engine is connected to the wheel. Mopeds have max power at, lets say 10.000 rpm (my Bultaco Astro 50cc is approx. at 11.500rpm). What factories do is connect the engine to the whaeel at maybe 5.000rpm, so there is litlle power. What you want to do is connect the engine to the wheel at higher rpm. This can be achieved by either making the interior part of the clutch ligther, drilling holes, or changing the springs for harder ones, so that you need more rpm and foce to connect the engine to the wheel. Please e-mail me if you want more info.

Sergi Grum

RE: Why are sprints so fast??

twowheelers /

Yet another expert..

RE: Why are sprints so fast??

What's the matter "twowheelers"...... are you embarassed that a 15 year old kid knows more than you do?..... Because I would say he does...... Young Sergi has a VERY GOOD understanding of how his centrifugal clutch works..... and of how to modify it....... He also explained it quite well.... better than many adults.......And remember that English is probably his second language..... what other language do you speak?...... a lot of the time young men talk about mechanical stuff and are badly misinformed..... Not Sergi !!

Hello Sergi...... Good explanation !..... You have a good understanding of mechanics........ Maybe someday you will be a motor "tuner" for another 500cc GP Roadracing Champion like Alex Criville.... I wish my country (USA) was a bigger fan for roadracing like your country..... though KRjr will be bringing the Champ back here this year !... Go USA!

For those of you that do not know Sergi comes from a part of the world (Catalunya Spain) that absolutely LOVES 2-stroke motorcycle Grand Prix roadracing.....maybe thats why he knows his motors?

RE: Why are sprints so fast??

twowheelers /

Hello Fred. It's nice to finally hear someone who doesn't know @!#$ about the topic and is simply babbling to show off is immense ego. If you had carefully read the text, you would clearly see that Sergi has perfectly explained the principles of the centrifugal clutch, but entirelly missed the topic. And the topic was "why can Sprints go faster than Targas?". As you may or more likely may not know, Tomos mopeds don't have variomatic transmission, so all that "science" about increasing the rpms for the clutch to "connect to the wheel" simply isn't applicable in connection with Tomos geared transmission. If you had a manual geared moped (which I'm sure you don't have because you wouldn't be so "smart" regarding this if you had one), you could easily test his theory by revving the engine to 5000 rpm and dumping the clutch. At least I know what would happen next. You don't, because as previously said you don't know @!#$ (OK, you've learned about the centrifugal clutch). I wonder if you could tell the difference between a variomatic belt and a gear wheel.

Unfortunately it appears that you haven't encountered any educated adults in your life as physics of centrifugal forces is a matter of basic education. You say that "young men talk about mechanical stuff and are badly misinformed"? Would that mean that USA doesn't know the term "book"? You also seem to be very patronizing to people, who's native language isn't English. That would also include me then. Patronise me please, it sounds so good!

But you have really outdone yourself in that last paragraph teaching all "those that do not know" of your excellent knowledge and experience in GP as well as your profound geographical expertise. What a marvellous boy you are! Unfortunatelly the origin of you or Sergi doesn't decide the level of experience regarding any tuning techniques and in fact anything. If he comes from Spain, that doesn't mean he's some "super tuner" just because they race motorcycles there. Look at you for example- US is the largest motorcycle market in the world yet you wouldn't know how to shift into 1st gear on anything that moves on two, four or more wheels.

I would say Sergi doesn't exactly know more than me, but one thing is certain-If me and Sergi were drunk and stoned to death, we would still able to tell more about engines than you will know in 10 years from now.

RE: Why are sprints so fast??

god damn two wheeler, thats a bit harsh don't you think?

RE: Why are sprints so fast??

twowheelers /

I guess so. I had a bad day. Sorry :-)

RE: Why are sprints so fast??

Boy.... Talk about an EEEEEEGOOOO !!!...... whatsa matter 2-wheelers ... did I get you a little upset.... You weren't going to cry were you?....

First of all if you had simply had some useful info when you posted instead of saying......((((((( "another expert"))))))))..... which is nothing but a snotty kids retort..... I wouldn't have smacked you .

Second of all a centrifugal clutch (which a Tomos DOES HAVE inside its gearcase) can ABSOLUTELY be tuned to hit harder off the bottom ..... simply by making the "weights" lighter or increasing the tension on the springs....... and it doesn't have to be a "variomatic" belt-drive (we call them C-V's in the US) for this technique to be of some use..... remember the question was about why it accelerated better from a standstill but had the same top speed...... so with a later "engagement" at a higher RPM (higher HP also)... the ped will accelerate harder at the start of our little race..... and I guess you were trying to intimate that "the gosh durn thing would wheelie over backwards on your scared self"...... but that's very unlikely cause the ped doesn't have enough HP and the clutch won't hook up that positively...... It will however stay up at a higher RPM where there's more power till the ped's speed catches up with the clutch's speed.... which could be why that model accelerates harder than the other..... but it could be internal gearing also.....I will admit I don't know the diff. between the models.

Do I have a "moped" with a manual clutch? ...... Well it's not a ped (got them too) .... but will a Honda CBR600 F4 count?....... I tell you what.... you come on over and stand behind it while I hold the front brake on and dump the clutch while I hold the RPM at say 8000......"at least I would know what would happen next"....yeah ya putz.... you'd have hot bits of my rear tire sticking to your pompous self.

Do I know the difference between a V-belt and a gear wheel... yeah.... one of them is made of rubber like your head......... Do you know what the stoichiometric ratio for an internal comb. engine is supposed to be?...... Do you know what the speed of sound has to do with the dimensions of an 2-stroke exhaust pipe?.... Do you know which has a higher ultimate BMEP, a 2 stroke or a 4 stroke?

If my post sounded patronizing it's because I know a lot of young people, and a lot of people for whom English is not their forst language read this stuff, so I purposely write in a simplistic manner....is that wrong?

And as for me not even being able to shift gears..... my god man..... you have really got a bug stuck up your butt don't you?...... Why would you even try to guess at such a thing?...... In fact I have well over a hundred motorcycle racing trophies from tracks all over my corner of the world and have ridden down straightaways on roadrace tracks at over 135 mph shifting all 6 gears!!.....

One thing is for sure even if Sergi someday meet at a racetrack and get all drunk and stoned......... neither of us will ever be as big a jerk as you...... cause we love bikes...... you only love yourself....... (but I'm the one that has a big ego!!!....now that's funny! )

RE: Why are sprints so fast??

twowheelers /

See, there you go bragging again..

Your questions confirmed my assumption that you know nothing about engines. If you had known more, you would formulate them more specifically.

The stoichiometric ratio for an internal combustion engine depends on the propellant. I'll presume you were referring to petrol, so it's 1:14.7 (propellant/air). But if the engine is utilising a lean burn process, it can go over 1:60.

The sound velocity, which depends on the temperature of expanding gasses and specific heat ratio, is used for calculating the tuned lenght of a 2-stroke exhaust pipe.

Yet again I have to read your mind and presume you were referring to a Otto cycle 2 and 4 stroke engine of same displacement- in this case the 4 stroke has a higher "ultimate" BMEP due to closed gas circulation.

Yeah, and I'm supposed to believe that a goddamn engineer/tuner/racer US national champ Criville wannabe like you has the time to talk about centrifugal clutches in a moped forum..

another expert................... heeheeheehee

thanks for admitting you were wrong about the cent. clutch........hahahahah...... dude you are crackin me up now !!!.......hahahaheeheehee

another dumbhead................... heeheeheehee

twowheelers /

Think so? I was hoping that going into technicalities wasn't necessary, but hey, if you're so persistive so be it.

As I could have understood from his post, Sergi was describing a moped engine with a very narrow powerband and a very steep torque curve. This would in fact confirm his correct explanation of modifying the clutch so that it "hooks up" at higher rpm. But this is only applicable on engines with a narrow power band, which are utilising a large number of gears or a transmission with a continuously variable ratio, in his case a variomatic. With these types of transmission, the engine can run within the powerband at all or most of the time.

Transmissions with a small number of gears (like the 2-speed Tomos) are driven by engines, which need to have a wider powerband- for running within the powerband at all or most of the time. In short, they need to be elastic- this type of engine will be known to those who have drove something with big displacement and small number of cylinders, like a BMW Boxer or let's say a VTR 1000. Lots of torque, almost no need to shift. And consequently, less gears to build.

What this means is that if you tune the clutch on a 2-speed transmission to engage at higher rpms, you also have to shift the torque curve so that it's peak is reached at higher rpm. As you may or more likely may not know, Tomos mopeds have a very wide powerband, but more importantly, they also have a very flat torque curve. So if you would modify the clutch on a stock Tomos, you would gain nothing- the engine is producing 3.7 Nm of torque accross the whole curve, but this number starts to rise SOONER than the 1st speed clutch engagement point and therefore most of the torque is even available before the clutch engages. So if you would modify the clutch to engage let's say 1000 rpm higher, the engine would produce the same amount of torque at that point.

Unfortunatelly this would decrease acceleration- the engine would be revving up and waiting for the clutch to engage (after the torque peak) instead of pulling away at the torque peak at lower rpm. And even if you count out the time wasted for waiting for the clutch engagement, the acceleration would be exactly the same due to previously mentioned flat torque curve.

Therefore Sergi's explanation of the inner workings of the centrifugal clutch is correct, but his clutch tuning instructions aren't applicable on any stock(!) Tomos. But if you go changing the thermal unit and modifying the power band, that's a different story.. The clutch itself can't make miracles.

Maybe that was enough?

I've just been looking at the last things been written in this line of messages and I am very dissapointed. I never really wanted to create a heated up discussion on who knows more on whatever. I would like to thank Fred for his compliments, though. I just want to help Tim out, but after reading a bit more about Tomos, I've seen I might be incorrect about the reason for it having so much acceleration. You see, Tomos are inexistent in Spain, and I've only seen a few pictures of them on the Internet. By its looks I assume they had a centrifugal clutch, so I tried my best to explain the reason in my third language (first comes Catalan and Spanish). About 95% of the mopeds in Spain have some mod or other (80cc engines, etc..), so there is quite a tradition for modifying the mopeds.

Anyway, although I shall not discuss whether America has the largest moped market in the world, but I can say that mopeds are very popular in Spain and 50cc bikes in general. Racing them is also very popular, there is the Gilera Runner cup, for instance, where they get 140 km/h, besides many more 50 cc dirtbike competions. The CEV, Campeonato Espa

RE: Maybe that was enough?

don't worry chief. you did nothing but contribute to the community. all is well on the moped front. well except my moped isn't working right now. on the path to revival though.

unite, swarm, and destroy


-moped army-

ha ha

yet your gay

why is my bianchi slow?

Let me add my two-cents to this bizarre forum exchange. Perhaps Sergi can help me. Que tal, compa

RE: why is my bianchi slow?

this is what babelfish translated your spanish too.

" Sergi, if podeis to help me, super estare agradesido. I believe that quizas your endiendes but of this thing that demas. Instructions in Spanish or ingles this good. Quizas in ingles serious better, because alive in the U.S.A. and quizas not conoceria the translation of the instructions so that algun friend helps me in it. But also, quizas if. OK? And not either because both crazy they s'estan fighting! That small, no? Good, greetings companion. I hope that podeis to help me... already I am tired to walk so slow! -)"


proper translation ...

My spanish was a "private" msg to Sergi of sorts (as a fellow Spanish-speaker). But here is the translation, in the spirit of openes (apertura):

"Sergi, if you could help, I will be super thankful. I think that perhaps you understand more about these things than the rest. Instructions in Spanish or English are fine. Perhaps English would be better, for I live in the US and perhaps might not know the translation of the instructions so that some friend helps me with it. But also, perhaps yes. OK? Y also do not know why those two crazies are fighting with each other! What a riot, eh? Well, greetings comrade. I hope you can help me ... I'm already tired of going so slow! ;)"

Hope that helps. BTW, no offense to the two crazies. I just thought (as most of you probably do) that fighting over who knows more about mopeds was pretty silly. I will readily admit that I know nothing. So anyone that can help me is welcome to try. Ivo (also on forum) already gave me some tips. But please, the more the better!

RE: Why are sprints so fast??

Didac (Barcelona-Spain) /

Molt b

RE: Maybe that was enough?

Didac (Barcelona-Spain) /

Ho he llegit tot Sergi, no et preocupis, aquestes coses passen en els f

RE: Why are sprints so fast??

Good,controlled answer,Fred! I thought maybe you might get a little `outta' sorts' with the numbskull,but you just blew him away with ice-cold facts. Two Wheeler, learn to speak from a positon of knowledge. You are presumptuous to the Nth degree. I would rather have a 1969 Jawa tuned by Fred,than a `95 Goldwing that you have touched. I happen to know that the EXCELLENT motorcycle mechanic herein named Fred has tuned a variator for `It's Looking UP' and did a great job. You would do well to go to `resources',then `articles' and read and LEARN Fred's Guide on `How to Fix Your Moped'(BTW,since you're so presumptuous,this guide was PURPOSELY written simply for `newbies' to mopeding. I think he just wrote `How to Fix Your Mouth' directly to you, just now. Now go pick on an ant, because that's someone your own size. don-ohio (:^)

RE: why is my bianchi slow? translated to spanish

Didac (Barcelona-Spain) /

Well, I think it's admirable the dan's effort to write a message in spanish is admirable. I know my english is only a little better than his sapnish, but Ithink is a good idea to translate it into correct spanish:

Sergi, si puedes ayudarme te estar

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